Institute of Bio- and Nanosystems, IBN-4, Biomechanics, Research Centre Jülich GmbH, Jülich, Germany.
J Phys Condens Matter. 2010 May 19;22(19):194109. doi: 10.1088/0953-8984/22/19/194109. Epub 2010 Apr 26.
Mechanosensing is a vital prerequisite for dynamic remodeling of focal adhesions and cytoskeletal structures upon substrate deformation. For example, tissue formation, directed cell orientation or cell differentiation are regulated by such mechanosensing processes. Focal adhesions and the actin cytoskeleton are believed to be involved in these processes, but where mechanosensing molecules are located and how elastic substrate, focal adhesions and the cytoskeleton couple with each other upon substrate deformation still remains obscure. To approach these questions we have developed a sensitive method to apply defined spatially decaying deformation fields to cells cultivated on ultrasoft elastic substrates and to accurately quantify the resulting displacements of the actin cytoskeleton, focal adhesions, as well as the substrate. Displacement fields were recorded in live cell microscopy by tracking either signals from fluorescent proteins or marker particles in the substrate. As model cell type we used myofibroblasts. These cells are characterized by highly stable adhesion and force generating structures but are still able to detect mechanical signals with high sensitivity. We found a rigid connection between substrate and focal adhesions. Furthermore, stress fibers were found to be barely extendable almost over their whole lengths. Plastic deformation took place only at the very ends of actin filaments close to focal adhesions. As a result, this area became elongated without extension of existing actin filaments by polymerization. Both ends of the stress fibers were mechanically coupled with detectable plastic deformations on either site. Interestingly, traction force dependent substrate deformation fields remained mostly unaffected even when stress fiber elongations were released. These data argue for a location of mechanosensing proteins at the ends of actin stress fibers and describe, except for these domains, the whole system to be relatively rigid for tensile strain with a mechanical coupling between the front and rear end of a cell.
机械感知对于基质变形时黏着斑和细胞骨架结构的动态重塑是至关重要的。例如，组织形成、细胞定向或细胞分化受到这些机械感知过程的调节。黏着斑和肌动蛋白细胞骨架被认为参与了这些过程，但机械感知分子的位置以及弹性基质、黏着斑和细胞骨架在基质变形时如何相互耦合仍然不清楚。为了研究这些问题，我们开发了一种敏感的方法，可将定义的空间衰减变形场应用于在超软弹性基质上培养的细胞，并准确量化细胞骨架、黏着斑和基质的应变。通过跟踪基质中荧光蛋白或标记颗粒的信号，在活细胞显微镜中记录应变场。作为模型细胞类型，我们使用肌成纤维细胞。这些细胞的特点是具有高度稳定的黏附和产生力的结构，但仍然能够以高灵敏度检测机械信号。我们发现基质与黏着斑之间存在刚性连接。此外，发现应力纤维几乎在整个长度上都几乎没有可伸展性。只有在靠近黏着斑的肌动蛋白丝的末端才会发生塑性变形。因此，这个区域在不通过聚合延伸现有肌动蛋白丝的情况下被拉长。应力纤维的两端都与可检测的塑性变形在两端机械耦合。有趣的是，即使释放了应力纤维的伸长，依赖于牵引力的基质变形场仍然基本不受影响。这些数据表明机械感知蛋白位于肌动蛋白应力纤维的末端，并描述了除这些区域外，整个系统对于拉伸应变仍然相对刚性，细胞的前端和后端之间存在机械耦合。
